Binary molecular compounds are composed of only two elements.
Examples are H2O, NO, SF6 etc. . Naming these binary compounds
is a little bit more involved than naming salts. Why is this
so? Molecular compounds are more difficult to name because the
atoms combine through covalent and not ionic bonds. Therefore
we cannot use the electrical neutrality rule for these compounds.
Most molecular compounds are made from nonmetals.

Sometimes these compounds have generic or common names (e.g.,
H2O is "water") and they also have systematic names
(e.g., H2O, dihydrogen monoxide). The common name must be memorized.
The systematic name is more complicated but it has the advantage
that the formula of the compound can be deduced from the name.

Simple binary compounds consist of only a few atoms. Systematic
naming of these compounds follow the rules:

The elements , except for H, are are written in order of
increasing group number (e.g., NO not ON)

The number of atoms of a given type is designated by a prefix
such as di- , tri-, tetra- etc. (The exception to this rule is
for the first atom: if the first atom is "mono" then
no prefix for it is given.) (e.g., NO is nitrogen monoxide not
mononitrogen monoxide)